Nutritional compositions destined for feeding patients suffering from certain deficits or diseases often need to be fortified with specific amino acids or peptides. For example, leucine is an important ingredient for compositions intended for replenishing muscular tissue, see e.g. WO 01/58284. GB-A-2,292,522 discloses a preparation for supporting the immune system containing, inter alia, methionine, valine, leucine, threonine, phenylalanine, lysine, isoleucine and tryptophan. WO 2004/103383 discloses the use of leucine and glycine for the treatment of chronic wounds.
However, some amino acids have insufficient solubility, wettability, sinkability or dispersibility or a bad taste or a combination thereof. This applies especially to large neutral (hydrophobic) amino acids such as leucine, isoleucine, valine, phenylalanine, and tryptophan, and to the sulphur amino acids methionine and cysteine (or cystine). As a consequence, the production of such compositions is hampered with dissolution problems, and the compositions are poorly accepted because of their bad taste.
Prior art methods developed for overcoming this problem include encapsulation of the amino acids, e.g. using oils or other relatively hydrophobic materials, optionally combined with lecithins.
JP-A 2-042967 describes coating of amino acids or drugs with an ethanol or acetone solution of glycerol acetate or lecithin as a surfactant, followed by an oil and again the surfactant. U.S. Pat. No. 6,506,422 discloses a nutritional formula for PKU patients containing casein glycomacropeptide as protein source together with free amino acids including Tyr. The amino acids may be encapsulated with edible fats, such as hydrogenated palm oil. EP-A 363,879 suggests to mask the taste of free amino acids by combining them with candied fruit and a gelling agent such as starch or gums. US-A 2004/0148013 teaches to coat food material, such as amino acids, with an organic zinc salt and a high-melting fat. EP-A 388,237 discloses a coating for amino acids containing about 55% sugar, about 40% hardened fat and about 0.6% lecithin.